BACKGROUND: In patients with severe attacks of ulcerative colitis (UC), IV steroids represent the first-line treatment, leading to clinical improvement in approximately 50-60% of patients. AIM: The aim of this study was to prospectively compare the efficacy and safety of different modalities of steroid administration, and to evaluate predictors of failure to therapy. MATERIALS AND METHODS: In a single-center, double-blind trial, consecutive patients with a severe attack of UC received 1 mg/kg/day of 6-methyl-prednisolone administered randomly by either a bolus injection (group A) or continuous infusion (group B). RESULTS: Sixty-six patients were enrolled (35 men, mean age 38 +/- 15, range 18-75 yr), 15 of them at their first attack of UC; in the remaining cases, the mean duration of disease was 4.5 +/- 5 yr. At inclusion, forty patients (60%) had pancolitis and the remainder had left-sided colitis. Overall, thirty-three patients (50%) underwent clinical remission after 7 days of treatment: 16 of 32 in group A and 17 of 34 in group B. Thirty-one patients eventually underwent total colectomy (12 in group A and 9 in group B), which was carried out by the first month in 10 patients (5 in each group). Twenty-eight patients (15 in group A and 13 in group B) experienced steroid-related adverse reactions. All differences between groups were not statistically significant. Previous use of steroids (OR 13.6, CI 2-86) and active smoking (OR 11.6, CI 1.4-107) were independent predictors of nonresponse. CONCLUSIONS: In severe attacks of UC, methyl-prednisolone given as a continuous infusion was no better than bolus administration in terms of efficacy and safety.